The present invention relates to a method for manufacturing a preform and a preform for drawing a micro structured optical fiber.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Microstructured optical fibers, also known as a sub-class called Photonic Crystal Fibers (PCF), are optical wave guide conductors, in which the light is conducted through a light conducting core, around which (for example) capillaries are arranged, which extend respectively along the optical fiber. In one particular design, the capillaries exhibit a hexagonal symmetry as seen in a cross section of the optical fibers, with the core in the center.
Microstructured optical fibers are drawn principally from cylindrical preforms (blanks), which are heated at the end in a drawing apparatus, to draw the optical fiber from the heated end of the preform.
The established preforms are manufactured from a casing (jacket) in the form of a glass tube, in which (for example) a glass cylinder is coaxially arranged as a rotationally symmetric core element within the casing. Furthermore, hollow cylinders in form of glass tubes are positioned around the glass cylinders in the casing. In particular, the hollow cylinders may be arranged periodically around the glass cylinder (the core element) with hexagonal symmetry, the cross section thus forming a polygonal pattern. The casing, the hollow cylinders, and the glass cylinder (the core element) are then fused in such a manner to form an overall structure or an overall system, so that the cavities between them are at least partially eliminated.
Instead of hollow cylinders, corresponding solid cylinders may also be used.
The established procedure to manufacture a preform for drawing a microstructured optical fiber have the disadvantage that during fusing to an overall structure, the hollow or solid cylinders very often fracture and do not permit a stable, reproducible fusing along the length.
It would therefore be desirable and advantageous to provide an improved method for manufacturing a preform for drawing a microstructured optical fiber to eliminate the strong tendency to fracture during fusing, and to ensure a reproducible long-term, stable fusing.